Extrusion of metal tubing



Jan. 7, i964 l.. HOFFMANN ExTRUsVoN oF METAL TUBING 2 .Sheets-Sheet lFiled Dec. 22, 1960 INVENTOR LEO HOFFMANN AGENT.

Jan. 7, 1964 L. HFFMANN EXTRUSION OF METAL TUBING Filed Dec. 2.2, 1960 2Sheets-Sheet 2 E wm mv United States lPatent 3,116,834 EXTEUSHN GliMETAL TUBHNG Leo Heitmann, New York. NAZ., assigner to Baldwin-Lirnadlamilton Corporation, Philadelphia, Pa., a corporation ofPennsylvania Filed Elec. 22, weil, Ser. No. '77,619 6 Claims. 1{(Ii.207-10) This invention relates to the hot extrusion of metal tubing overa mandrel, and particularly to the extrusion of tubinfJ at relativelyhigh temperatures.

When producing tubes in the above manner, a heated billet is inserted ina container and the metal is then forced through an annular or similarlyshaped orifice formed by an apertured die in conjunction with a mandrel.In one conventional method the mandrel is stationary during extrusionand only the front part thereof projects into the opening of the die.Removal of the extruded tube from the front tip of such mandrel isrelatively easy, but the stationary tip is subject to high pressure andfriction at elevated temperatures for an extended period of time, whichresul-ts in pronounced wear. A necliing effect may occur and causedestruction of the tool.

in another conventional procedure the mandrel has a relatively longeffective portion and is gradually advanced in the die opening duringextrusion so that any wear will be distributed over a surface area ofsubstantial size and there is not much danger of localized overheating.vHow ever, it is difficult to strip such mandrel from the end of the tubeafter extrusion. This is due to the fact that during extrusion thetemperature of the tube material is considerably higher than that of themandrel and upon comple ion of the operation the tube shrinks quicklyupon the cooler tool. Sometimes, mandrels of this type have been taperedto facilitate the ow of metal over the mandrel during extrusion. Thiswould also tend to assist in the stripping operation but is generallynot sufficient alone to prevent freezing of the tube on the mandrel.Besides, the extruded tube will have a tapered inner wall and thus avarying Wall thickness throughout its length. This is not acceptable incases in which the inner wall of the tube must be cylindrical at leastover a major portion of its length.

lt is an object of the invention to avoid the aforesaid difficulties inthe hot extrusion of metal tubing in a simple and effective manner.

lt is also an object of the invention to provide means for minimizingthe shrinkage of extruded metal tubing upon a mandrel.

it is another object of the invention to facilitate stripping of amandrel after hot extrusion by varying the intercontour of extrudedtubing at the rear end thereof and to keep such variation small so thatthe entire length of the tubing may be used for the ultimate purpose forwhich the product is intended.

it is a further object of the invention to facilitate stripping of amandrel after hot extrusion by varying the internal contour of extrudedtubing amply at the rear end thereof and severing such rear end from themajor portion of the tubing after extrusion.

lt is also an object of the invention to provide an improved mandrel forhot extrusion, which is adapted to be gradually advanced in a dieopening at least during the maior portion of the operation but may bestripped easily from metal tubing extruded thereover.

One aspect of the invention involves the arrangement of an auxiliaryportion or relief shoulder on the mandrel. Shoulders have been providedon extrusion mandrels for various purposes in past but have not beendimenioned and arranged to minimize the freezing of tubing on mandrels.

alienati Further objects, features and advantages of the invention willbecome apparent as the description proceeds.

In the drawings which illustrate certain embodiments of the invention byway of example,

FIG. l is a diagrammatic, fragmentary section through an improved metaltube extrusion press showing the parts in an initial stage of theoperation, certain dimensions being exaggerated for better illustration;

FlG. 2 is a section similar to FlG. 1 but showing the parts at the endof the extrusion;

FIG. 3 is a section showing the rear end of an extruded tube andillustrates a modified procedure;

FIG. 4 is a section similar to FIG. 2 but shows a further modification.

Referring to FlG. l of the drawings, the extrusion apparatus illustratedtherein comprises a container lil adapted to receive a heated billet orcharge 12 to which pressure is applied by a stem or plunger ld with theaid of a dummy block 16. rThe stern la has a bore i3 therethrough toreceive and guide a movable mandrel holder Ztl.

A movable mandrel generally indicated at 3@ comprises a relatively longmain or front portion 32 and a normally shorter auxiliary portion in theform of an auxiliary or relief shoulder or collar 34 positioned adjacentthe rear end of the main portion 32. The cross section of shoulder 34 issimilar' to, but slightly lmger than, the cross section of portion 32.Mandrel Sil passes through a bore 36 of dummy block lo and is attachedto its holder Ztl at 3S. The main mandrel portion 32 is sufficientlylong to extend at least through the major portion of billet l2.

A die dil is mounted on a support d2 and has an opening, the narrowestportion 44 of which forms an annular extrusion orifice in conjunctionwith mandrel 30.

The billet l2 when loaded in the container may either be hollow toaccommodate the mandrel 3th, or it may be solid and then pierced in thecontainer by applying pressure to the mandrel holder 2li, the mandrel 3dbeing in each case advanced through the billet until the tip of itsfront portion 32 is positioned in portion i4 of the die opening, atwhich time the shoulder 3d has entered the rear portion of the billet.Upon application of pressure to stem 14, the billet will first be causedto bear against the wall of the container as well as against bothmandrel portions 32, 34 and will then be forced to flow through theextrusion orifice between mandrel portion 32 and die d@ to form a tubegenerally indicated at Sii. The mandrel is gradually advanced togetherwith stem i4 by means of the holder 2@ so that successive parts of themain mandrel portion 32 will cooperate with the die. lt will be clearthat during this stage of the operation which is illustrated in PEG. 1,the inner contour of tube 5d will correspond to the cross section of themain mandrel portion 32 while the outer contour of the tube will bedetermined by the inner contour of the die opening at its narrowestportion 44. The opening of die @il and the main portion 32 of themandrel are dimensioned so that at room ternperature the extruded tubewill have a prescribed or selected or nominal cross sectional size.

ln the past the operation has normsdly been con in the manner describeduntil completion of ex As indicated hereinbefore, this would result inthe hot material of the tube shrinking upon the cooler mandrel 3@ alongthe entire length of the mandrel portion 32 which is cylindrical in theembodiment describe. to obthe maior tain a substant .ny uniform wallthickness i' portion of tube 5d, and it would be very difficult towithdraw the mandrel by means of its holder at the end of the extrusionfor stript the mandrel from the tube. The temperature difference e'twcenthe tube and mandrel and the corresponding shrinkage effect will beoarticuiarly pronounced if the mandrel is of the type eelt pped withinternal passages for the circulation of a cooling mediun According tothe intention, shrinkage of the tube upon *the mandrel is minimized in asimple and effective manner. After the major portion of the tube hasbeen extruded, tl e inner contour of the extrusion orice is enlarged toan extent sulieient to compensate for a predetermined amount ofshrinkage which will occur in the area of the rear end of the tube afterextrusion, and the :remainder of the tube is then extruded through themodi- `fied orifice. The change in the orifice occurs when the yshoulder34 of mandrel Sti enters the narrowest portion of the die aperture. Toobtain the desired elect, the ldiarnetrical size of shoulder 34 shouldbe generally on the order determined by the equation d=d (1-i-c delta)'wherein d represents the diameter of shoulder 34, d the diameter of themain portion 32 of the mandrel, c the `Coc'jicien ol linear expansion(and contraction) of the m rial of the tube per unit of length andtemperature, .and delta a predetermined average drop in temperature `ofthe tube upon completion of the extrusion or more 'precisely in theperiod of time extending from extrusion 'to stripping. It in the saineinterval the temperature of `the mandrel likewise changes considerably,this should be taken into consideration and the shrinkage of the tube:should then be detemined relative to the mandrel. For example, if themandrel cools down somewhat after extrusion and before stripping andthus contracts to a cerztain extent, this may be deducted from theexpected ab- :solute shrinkage of the tube, but in case the temperatureof the mandrel increases due to absorption of heat from t he tube andthe mandrel thus expands, this will be equiv- .aient to an increase inshrinkage of the tube so that the .amount to be compensated for shouldbe augmented afcordingly. The change in the diametrical dimension of'the mandrel, of course, follows from its coetiicient of linearexpansion and the expected change in its tempera- *.ture.

As the coeilcient of linear expansion of a material norimally variessomewhat in dilerent temperature ranges, it 'may be found expedient forexact calculations to use an :average value when handling metals such ascopper, v.copper alloys, and steel which are extruded at high tem-,peratures With the mandrel shaped in the manner described the last endof the tube will be extruded with an enlarged inside diameter tocompensate for expected shinkage relative to the mandrel in the area ofthe tube end as ;shown in FIG. 2. ln the drawings a lirst, prescribedhole Aor bore of tube 5d extending through the major portion thereof isindicated at 52 while a second, slightly larger hole or bore at the rearend of the tube is indicated at :54. It will be clear that the size ofbore 54 is such that .after a predetermined shrinkage the tube end willstill clear, or barely touch, the relatively long main portion 32 of themandrel. lt may also be said that the bores S2, .5d are dimensioned sothat the LD. of bore measured lduring stripping will generally be on theorder of the LD. oi bore 52 measured during extrusion.

'\Viien, `lor example, tubing of 3 LD. is extruded from Vbrass having alinear coefficient of expansion (and contraction) per unit of length andper degree F. of about 00601 and the temperature differential deltaamounts to '1GCO F., the diameter of shoulder will be determinedapproximately by the equation (1+.ccoo1x1eom in zsns in.

Thus, bore 5d will be only ab ut .03 larger in diameter than bore 52 andthe complete length of the extruded tube including the slightly modiliedrear end thereof will often be found acceptable for practical use, inparticular if a drawing operation is carried out after extrusion.

Preferably, the diameter d' of shoulder 34 exceeds the calculated amountslightly but if it is desired to keep ,changes in Vthe inner contour ofthe tube to a minimum,

dialnet r d may closely correspond to the calculated dimension. a

The diterencc in size of holes 52 and 56 is shown cxaggerated in thedrawings for better illustration.

The length of tube extruded over shoulder 3:2., i.e., the length of bore54, should be such that the smaller bore 52 no longer surrounds the mainmandrel portion 32 when the extrusion is completed. At this time, firmcontact between tube and mandrel will occur only aY the shoulder 34 overa short distance resulting in a very limited amount of friction so thatstripping of the mandrel from the tube will be easy. lf desired, theshoulder 34 proper may be slightly tapered to additionally facilitatestripping and this will in no way atleet uniformity of wall thicknessobtained in the major portion of the tube along its bore S2.

in the embodiment of FIGS. l and 2 mandrel 3d is arranged for movementin unison with stem throughout the extrusion, including the last stageof the operation when the auxiliary shoulder 34 has entered the dieopening and cooperates therewith. Keeping in mind that bore 52 of t xetube should clear mandrel portion 3?. at the end of the extrusion, thelarger bore S4 should then extend along the length L of mandrel portion32 and further along the relatively short distance L by which shoulder34 will protrude from the narrowest portion 44 of the die Opening in theposition of the parts shown in FIG. 2, i.e., the length of bore 54should substantially equal L-l-L. Since, as stated, mandrel 30 travelsin unison with stem lf2', the extruded length of bore 54 will also beequal to Lr, wherein r is the extrusion ratio in the region of bore 54,that is, the relation of the cross sectional area of the billet to thecross sectional area of the tube at the rear end thereof. t follows thatthe distance L should be on the order determined by the equationPreferably the distance L will be made slightly greater than calculatedso that the bore 54 will be somewhat longer than required to make sureContact between thc wall of bore 5?. and mandrel portion 32 will beavoided at the end of the extrusion.

For example, when extruding the aforementioned brass tubes of 3 I.D. atan extrusion ratio of 2l with the portion 32 of the mandrel being 2Glong, the length L will be on the order determined by the equationInstead of continuing to move the mandrel forward after shoulder 34 hasentered the narrowest portion 44 of the die opening, the mandrel may bestopped at this instant. This will reduce the area of contact betweenthe extruded tube and shoulder 34 at the time stripping is carried out.It is true that wear will be increased somewhat at the shoulder 34 whenthe latter is stationary during extrusion, but this will not have severeconsequences since only a limited amount of material passes overshoulder 34. The length of the portion of billet l2 to be extruded overthe auxiliary shoulder under these conditions, i.e., with the shoulderin a stationary position, will be approximately equal to L/ r. This isanalogous to the foregoing equation lor L when neglecting any smalldistance through which, in a stationary position, the shoulder 34 mayproject from the narrowest portion 44 of the die opening.

FIG. 3 illustrates an extruded tube after it has been severed, at theterminal face shown at the right in FIG. 3, from remnant S6 (FIG. 2) ofthe billet in any suitable conventional manner and removed from thepress. As indicated hereinbefore, in accordance with one aspect of theinvention the portion having the enlarged bore 54 therein inf-1 in.

is retained as an integral part of the tube since frequently a slightvariation in internal diameter will be found acceptable for practicalpurposes. However, a modified procedure may be used under certainconditions. If the requirements are exacting and the tube must have auniform internal diameter throughout its length, or if the use of thefull length extruded is not planned for other reasons, the end of thetube hhaving the enlarged bore 54 may be cut off approximately in theplane indicated at 58. When using this procedure, of course, the size ofbore 54 need not be held within close limits and the diameter ofshoulder 34 may then be determined in a somewhat liberal manner so thatduring stripping there will be ample play between the wall of bore 54and the circumference of the main mandrel portion 32.

Another modification of the invention is shown in FIG. 4 in whichvarious elements retained from FIGS. l and 2 without change aredesignated by like reference characters. T he modified mandrel generallyindicated at 7 ti which includes a main portion 72 and an auxiliary orrelief shoulder 74 is equipped with a cutting shoulder or collar 76, thelatter fitting snugly in the narrowest portion 44 of the die opening aswell known in the art. The parts are illustrated in the position at theend of the extrusion in which mandrels of this type and their holdersare normally locked in the forward direction to prevent entrance of thecutting shoulder in the die opening prematurely during extrusion. Afterthe mandrel 70 and its holder 2t) have been released, they are advancedby applying pressure to holder 2% so that the cutting shoulder 76 willenter the die opening to push the extruded tube out of the die andthereby sever it from the remainder Se of the billet. The use of therelief shoulder 74 is of particular significance in combination with thecutting shoulder 76 since here stripping of the mandrel will be delayedby releasing the mandrel from its locked position and advancing itduring the shearing step. Due to this delay the tendency of the tube toshrink will be more pronounced when the cutting shoulder is used and thetube may contract to a degree making stripping extremely difiicult orimpo-ssible if the relief shoulder 74 is not employed.

As shown in FIG. 4, the main portion 72 may include a short conicalportion 78 to provide for a smooth connection with the auxiliaryshoulder 74. The tube generally indicated at 8@ will then have a taperedportion between the bores 82 and 84 thereof as shown at 86.

In cases where the wall thickness need not be entirely uniform even inthe major portion of the tube, the invention may be used in combinationwith a slight taper of the main portion of the mandrel to facilitateextrusion. Ease in stripping will be insured by means of the auxiliaryshoulder 34, and the taper of the main portion 32 will be very limited.

Wherever the expression tubing is used in the description and claims, itshould be interpreted as including hollow shapes of circular ornon-circular cross section.

While certain preferred embodiments of the invention have beendescribed, it will be understood that various modifications and changesmay be made without departing from the scope and spirit of the inventionas defined in the appended claims.

Having described my invention, what I claim and desire to secure byLetters Patent is:

1. In a method of extruding metal tubingfrom a heated billet, the stepsof extruding the major portion of said tubing through an orifice ofannular type having original o-uter and inner contours corresponding toa selected outer and a first inner contour of said tubing, thenenlarging the inner contour of the orifice, and extruding the remainderof said tubing with a second inner contour determined by said enlargedinner contour of the orifice, the difference between the original andenlarged inner contours of said orifice and the corresponding differencebetween the first and second inner contours of said tubing being suchthat upon a predetermined shrinkage at the end of the extrusion the sizeof said second inner contour of the tubing will generally be on theorder of the size of said first inner contour measured during extrusion.

2. In a method of producing metal tubing over a mandrel from a heatedbillet, the steps of extruding the major portion of said tubing throughan orifice of annular type having outer and inner contours correspondingto a selected shape of said tubing, then enlarging the inner contour ofthe orifice to an extent at least sufficient to compensate for apredetermined amount of shrinkage of the tubing after extrusion, andextruding the last portion of said tubing with an inner contourdetermined by said enlarged inner contour of the orifice over a lengthat least suiiicient to completely clear said mandrel outside saidorifice.

3. A method as specified in claim 2, including the step of severing saidlast extruded portion of the tubing from said major extruded portionthereof.

4. In a press for the extrusion of metal tubing from a heated billet, adie having an opening therethrough, a mandrel movable into said openingof the die to form an extrusion orifice between said die and mandrel;said mandrel having a main portion adapted to extend at least throughthe major portion of the length of said billet and shaped to produce aprescribed inner contour of said tubing, and a relatively shorteffective auxiliary portion adjacent the rear end of said main portion,the cross section of the auxiliary portion exceeding the cross sectionof said main portion to an extent suiiicient to compensate for apredetermined amount of shrinkage of said tubing relative to said mainportion of the mandrel; and means for advancing said mandrel throughsaid die during extrusion, whereby the tubing will first be formed oversuccessive parts of said main portion of the mandrel to receive saidprescribed inner contour but the rear end of the tubing will be formedover said auxiliary portion of the mandrel to receive an inner contourenlarged in accordance with the size of said auxiliary portion tominimize shrinkage of the tubing upon the mandrel after extrusion.

5. A press as specified in claim 4, wherein said mandrel i includes acutting shoulder for severing extruded metal tubing from residue of saidheated billet, said cutting shoulder being located adjacent the rear endof said relatively short eective auxiliary portion of said mandrel.

6. A press as specified in claim 4, in which the die opening has anarrowest portion, and the length of the auxiliary portion of themandrel projecting from said narrowest portion of the die opening at theend of the extrusion is on the order of wherein L is the length of themain mandrel portion, and r the extrusion ratio prevailing duringformation of the rear end of the tubing and representing the relation ofthe cross sectional area of the billet to the cross sectional area ofsaid rear end of the tubing.

References Cited in the file of this patent UNITED STATES PATENTS1,664,990 Oehmig et al Apr. 3, 1928 1,854,411 Leighton Apr. 19, 1932FOREIGN PATENTS 898,884 Germany Dec. 7, 1953

1. IN A METHOD OF EXTRUDING METAL TUBING FROM A HEATED BILLET, THE STEPSOF EXTRUDING THE MAJOR PORTION OF SAID TUBING THROUGH AN ORIFICE OFANNULAR TYPE HAVING ORIGINAL OUTER AND INNER CONTOURS CORRESPONDING TO ASELECTED OUTER AND A FIRST INNER CONTOUR OF SAID TUBING, THEN ENLARGINGTHE INNER CONTOUR OF THE ORIFICE, AND EXTRUDING THE REMAINDER OF SAIDTUBING WITH A SECOND INNER CONTOUR DETERMINED BY SAID ENLARGED INNERCONTOUR OF THE ORIFICE, THE DIFFERENCE BETWEEN THE ORIGINAL AND ENLARGEDINNER CONTOURS OF SAID ORFICE AND THE OCRRESPONDING DIFFERENCE BETWEENTHE FIRST AND SECOND INNER CONTOURS OF SAID TUBING BEING SUCH THAT UPONA PREDETERMINED SHRINKAGE AT THE END OF THE EXTRUSION THE SIZE OF SAIDSECOND INNER CONTOUR OF THE TUBING WILL GENERALLY BE ON THE ORDER OF THESIZE OF SAID FIRST INNER CONTOUR MEASURED DURING EXTRUSION.